Dental caries is an infectious disease which the principal etiologic agent is Streptococcus mutans. Studies aimed at inducing immunity against most infectious diseases, including dental caries, have provided valuable information on microbial antigens important in inducing protective responses, the role of IgA antibodies in defense against infections which invade through or colonize on surfaces bathed by external secretions and in mechanisms involved in the induction of immune responses. Concurrent with these studies, the recent advancements in recombinant DNA technology and gene cloning have led to additional information on microbial gene products important in virulence and to the development of novel vaccines. The overall objective of the studies proposed in this application is to determine at the humoral and cellular levels the mechanisms involved in responses to oral vaccines consisting of recombinant, avirulent, safe Salmonella strains harboring expression vectors encoding cloned gene products of mutans streptococci which are important in caries immunity in an experimental rat model. Dose response studies using Salmonella vaccines and both germfree and conventional rats will be performed to determine: 1) the potential of orally administered Salmonella vaccines in inducing mucosal and/or systemic responses; 2) the nature (level isotype and specificity) of the responses induced in serum and secretions; 3) the dose of vaccine which induces the highest antibody response (especially salivary) to the cloned antigens of mutans streptococci; and 4) the effectiveness of the response in protection against infection with virulent mutans streptococci. We will characterize humoral and cellular aspects of responses to orally administered avirulent Salmonella and avirulent Salmonella vaccines expressing cloned gene products of mutans streptococci, in order to determine if mechanisms involved in response to the gram- negative microorganism influence the induction of responses to the expressed cloned gene products. In these studies, we will assess: 1) the level, isotype and specificity of antibody in serum and external secretions by ELISA; 2) the number, isotype and specificity of antibody-producing cells in various tissues by the ELISPOT assay; 3) the induction and characterization of T cells with specificity to the cloned antigens of mutans streptococci in vitro proliferative and antibody response assays; 4) the uptake of the avirulent Salmonella by rat Peyer's patches (major IgA inductive sites) and their dissemination to peripheral tissue by electron and immunofluorescence microscopy and by microbiologic analyses; 5) delayed-type hypersensitivity to Salmonella antigen; and 6) protection of rats against challenge with virulent Salmonella or mutans streptococci following a primary and secondary immunization. The effect of the amount of cloned antigen expressed and of co-expression of cloned potential adjuvants and mutans streptococcal antigens by avirulent Salmonella vaccines on inducing caries immunity will also be assessed. These studies will define immune mechanism at the T and B cell levels which are involved in responses to avirulent Salmonella and to expressed cloned gene products and should define cloned gene products of mutans streptococci important in caries immunity. These results should facilitate the development of similar oral vaccines which are effective in inducing immunity against a variety of infectious diseases.